The following lines from Book V of Paradise Lost, starting at line 180, are quoted in Kuipers’ book:

Air and ye elements, the eldest birth Of nature’s womb, that in quaternion run Perpetual circle, multiform, and mix And nourish all things, let your ceaseless change Vary to our great maker still new praise.

When I see quaternion I naturally think of Hamilton’s extension of the complex numbers, discovered in 1843. Paradise Lost, however, was published in 1667.

Milton uses quaternion to refer to the four elements of antiquity: air, earth, water, and fire. The last three are “the eldest birth of nature’s womb” because they are mentioned in Genesis before air is mentioned.

The book “Vectors” by Moon and Spencer (1964) has a great introductory chapter about the history of complex numbers, quaternions, and vectors. Vectors were seen as low-brow by the supporters of quaternions, but which one is a quaint mathematical oddity now?

Have fun with Paradise Lost. I’ve tried at around five separate occasions to read it and at best got half way through. It’s dense and difficult. But that’s probably true of Quaternions and Rotation Sequences, as well.